Why does a good absorber

And although they are clear, I cannot tease out the answer to my question. Improve this question. Add a comment. Active Oldest Votes.

Improve this answer. Thomas Fritsch Thomas Fritsch 21k 9 9 gold badges 49 49 silver badges 75 75 bronze badges. As my question specifically asked for a quantitative solution, you did answer that.

However I was hoping for an equation that gave me insight into how much hotter a black object would get than a white object. My initial sentence speculated that black objects get hotter than white ones. But it is also a poor emitter. Experience tells me otherwise. The answer lies in the fact that absorptivity and emissivity are frequency and temperature dependent for real objects.

If you feel I was vague or the question was poorly stated, I will ask it differently. Philip Wood Philip Wood 23k 3 3 gold badges 22 22 silver badges 49 49 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Darker materials also emit radiation more readily than light-colored materials, so they cool faster. You may be tempted to skip coating half of the card with the silver marker.

After all, that half is probably white , which indicates that it reflects light in the visible portion of the electromagnetic spectrum. The name " black body" is given because it absorbs radiation in all frequencies, not because it only absorbs. It is an ideal emitter : at every frequency, it emits as much or more thermal radiative energy as any other body at the same temperature.

In fact, black surfaces absorb almost all light. When an object absorbs light, it converts that light to thermal energy, and emits it back out as heat.

So, because black objects absorb more light, they also emit more heat. That's why wearing a black shirt on a hot, sunny day will only make you hotter.

Prior to Kirchhoff's studies, it was known that for total heat radiation, the ratio of emissive power to absorptive ratio was the same for all bodies emitting and absorbing thermal radiation in thermodynamic equilibrium. This means that a good absorber is a good emitter. Naturally, a good reflector is a poor absorber. Different surfaces You can see that dull surfaces are good absorbers and emitters of infrared radiation. Shiny surfaces are poor absorbers and emitters but they are good reflectors of infrared radiation.

When exposed to sunlight for a reasonable amount of time they absorb energy and heat up. The amount of energy absorbed and radiated is decided by the colour.

White is a good reflector while black is a good absorber of heat. Among other colours there is a gradation of temperature.

Black body radiation. All objects are continually absorbing and emitting infrared radiation. Black bodies are perfect absorbers and emitters of radiation. Message Board Thread - " color and emissivity " Color visible and emissivity infrared are not directly correlated.

In the visible range, color is the result of reflexion of light. Emissivity represents the ability of a material to emit heat, compared to what a theoretical body called a blackbody does. Since the primary source of infrared radiation is heat or thermal radiation , any object which has a temperature radiates in the infrared.

Even objects that we think of as being very cold, such as an ice cube, emit infrared. The warmer the object, the more infrared radiation it emits. Radiant energy is the energy of electromagnetic waves. The term is most commonly used in the fields of radiometry, solar energy , heating and lighting, but is also used less frequently in other fields such as telecommunications.

A blackened surface is an excellent emitter as well as an excellent absorber. The law states that at a given temperature the coefficient of absorption of a body is equal to its coefficient of emission.

A black body is an example of a good absorber of heat as well as a good emitter of heat. The outer layer of fabric does get hotter because the black color absorbs more heat.

But thin black clothing transmits that heat to the skin, making a person hotter. To sum up: Light-colored clothes in the summertime during the day, and get naked at night. Black or dark colored materials and objects radiate give off and absorb heat the fastest.

The reason for this is that lighter colors reflect more light. Instead of thinking of dark colors as absorbers of heat, darker colors are actually better absorbers of light. A black body is an idealized object that absorbs all electromagnetic radiation it comes in contact with. It then emits thermal radiation in a continuous spectrum according to its temperature.

Stars behave approximately like blackbodies, and this concept explains why there are different colors of stars. The color a person perceives indicates the wavelength of light being reflected. White light contains all the wavelengths of the visible spectrum, so when the color white is being reflected, that means all wavelengths are being reflected and none of them absorbed, making white the most reflective color.

Light energy can be converted into heat energy. A black object absorbs all wavelengths of light and converts them into heat, so the object gets warm. A white object reflects all wavelengths of light, so the light is not converted into heat and the temperature of the object does not increase noticeably. When heat radiation fall on polished surface or white objects, most of the heat energy is reflected black but when these heat energy are absorbed and very less amount of energy is reflect back apart from this black body absorbs more heat because black colours absorbs all colours of light energy, the more light is.

Black body is a perfect absorber and perfect radiator of energy. They can emit and absorb all frequencies. At a particular temperature it would emit maximum amount of energy possible for that temperature. When exposed to sunlight for a reasonable amount of time they absorb energy and heat up. White is a good reflector while black is a good absorber of heat.

Among other colours there is a gradation of temperature. Three factors determine how good a material is at absorbing and storing heat. The ideal material is: dense and heavy, so it can absorb and store significant amounts of heat lighter materials, such as wood, absorb less heat has a dark surface, a textured surface or both helping it absorb and re-radiate heat.